Modal diameter control of linear isothermal optical fibers

Abstract

In this paper, a simulation-based investigation of a strategy to control optical fiber diameter variations is reported. The proposed control scheme is based on the principles of modal control. A model of the fiber manufacture is presented and its sensitivity to the fiber draw speed is demonstrated. A control methodology, utilizing the basic concepts of modal control approach, is attempted on the linear isothermal optical fiber model, and this approach is shown to yield satisfactory results. The proposed approach can be modified and extended for nonlinear control of the fiber diameter.Optical fibers are currently used in diverse applications such as biomedical instrumentation, comunicationS, and space applications. These fibers are usually manufactured by the drawing process. In the single fiber drawing process, a glass preform, of acceptable physical and optical properties, is fed into a fumace, and heated until it becomes soft. The temperature at which the preform is soft enough for drawing fibers, ranges from 1500 to 2 5 W C, depending on the physical properties of the particular glass preform [ 11. The soft. glass is then pulled by means of a winder to form optical fiber. The performance of optical fibers and related optical components depends critically on the evenness of the fiber diameter [2]. Very precise control of the fiber diameter, therefore, is an important manufacturing consideration. Sufficiently large winder speeds have been shown to induce a hydrodynamic instability in the steady fiber flow, called draw resonance [3]. It is known that this instability causes periodic variations in the fiber diameter, which degrade product performance, and may even cause fiber breakage [4].Experimental work with polymers [5.6] has shown that the most significant parameter affecting the onset of draw resonance is the fiber draw ratio U, which is the ratio of the logarithms of the final and initial fiber velocities. This was confirmed theoretically through linearized perturbation analyses [7.8]. In addition, the fiber drawing process is also susceptible to small external disturbances, resulting from unsteady preform feed-in rates, heat sources and sinks. and noise induced vibrations. The effects of these disturbances are as important as the effect of winder speed variations [2]. The need to improve product quality and yield of the drawing process has motivated numerous investigations of modeling and stability analysis of the process [2-201, and several attempts to devise better diameter controllers [21-261.Imoto and coworkers [21,25] devised an optical fiber drawing process which features a gas flow controlling system, in addition to the drawing speed controlling system. Gas flow in the fumace is regulated such that faster fluctuations in fiber diameter are controlled, and the winder speed is varied such that slower fluctuations are reduced. It i s reported that the system works well, even in the presence of large changes in the preform feed-in velocity. Smithgd [23] applied optimization theory, based on a mean squar...

Dynamic Control of a Fiber Manufacturing Process using Deep Reinforcement Learning

“…Many of them focused on maintaining a steady diameter. Mulpur and Thompson developed a modal diameter control method based on simulation [15]. They assumed isothermal temperature profiles and utilized modal control method.…”